1. Field of the Invention
The present invention relates to roller drive control methods of fixing apparatuses and fixing apparatuses in electrophotographic image forming apparatuses.
2. Description of the Related Art
In this type of fixing apparatus, while recording paper is sandwiched and transported in a nip region between a pair of fixing rollers, the recording paper is subjected to heat and pressure by the fixing rollers so as to thermally fuse and fix toner onto the recording paper.
However, not all the toner is fused and fixedly attached onto the recording paper by the fixing process, and a small amount of toner transfers and adheres to the fixing roller side since the fixing rollers have a high surface temperature. For this reason, ordinarily a cleaning apparatus is provided that removes residual toner on the fixing rollers.
Conventional cleaning apparatuses involve removing residual toner on the fixing rollers using blade cleaning or felt cleaning or the like, but with techniques such as these, even when residual toner on the fixing rollers is removed, toner that has once adhered to the blade or the felt sometimes ends up returning to the fixing rollers.
Consequently, web cleaning techniques have been proposed. In these web cleaning techniques, a web sheet constituted by a thin cloth is wound onto a feed-out roller and one end of the web sheet is connected to a take-up roller, then the web sheet is fed out from the feed-out roller and is taken up by the take-up roller and the web sheet is caused contact the fixing rollers during the feeding out and taking up so as to remove extraneous matter on the fixing rollers.
On the other hand, sometimes recording paper that has passed through the nip region stays adhered to the fixing rollers and does not separate. For this reason, as shown in FIG. 6, a separation claw 202 is provided in a vicinity of a surface of a fixing roller 201, and a leading edge of the recording paper is separated from the surface of the fixing roller 201 by the separation claw 202. A leading edge of the separation claw 202 is formed having an acute angle such that this leading edge of the separation claw 202 inserts easily between the leading edge of the recording paper and the surface of the fixing roller 201.
Furthermore, in FIG. 6 the surface of the separation claw 202 that opposes the surface of the fixing roller 201 is formed flat, but this surface may be formed in a concave shape so as to skirt the surface of the fixing roller 201 such that the separation claw 202 is arranged even closer to the surface of the fixing roller 201 and so that the leading edge of the separation claw 202 inserts easily between the leading edge of the recording paper and the surface of the fixing roller 201.
However, it is necessary for this separation claw to be provided in a vicinity of the nip region between the fixing rollers, and the arrangement position thereof is upstream from the cleaning apparatus in the rotation direction of the fixing rollers. Thus, before the residual toner on the fixing rollers is removed, a portion of it adheres to the separation claw such that a large amount of toner adheres to and accumulates on the separation claw.
When the separation claw makes contact with the leading edge of the recording paper that has come passing through the nip region, the toner that has adhered to and accumulated on the separation claw ends up adhering to and soiling the leading edge of the recording paper.
Furthermore, when a lump of toner that has adhered to and accumulated on the separation claw becomes large, it may drop and adhere to the surface of the fixing rollers. The large lump of toner on the surface of the fixing rollers cannot be fully removed by the cleaning apparatus at one time and may get stuck with peripheral components such as temperature detecting thermistors provided around the surface of the fixing rollers, which may be a cause of damage to the peripheral components.
For this reason, a heater is provided in the separation claw in JP 2003-156967A to heat the separation claw and even when toner adheres to the separation claw, the toner is immediately heated and melted so as to return to the surface of the fixing rollers. This discourages soiling of the leading edge of the recording paper and damage to peripheral components by adhesion of large lumps of toner to the surface of the fixing rollers.
However, when using a heater to heat the separation claw in the manner of JP 2003-156967A, it is necessary to provide a sensor to detect the temperature of the separation claw and to control the temperature of the separation claw, which makes it impossible to avoid increasing the number of components and complicating the control thereof.
Furthermore, along with increasing speeds in image forming apparatuses there have been increasing numbers of sheets of recording paper to be processed by the fixing apparatuses, which increases the amount of heat of the fixing rollers, and since the power consumption involved for that has increased close to the rating for commercial AC power, it is undesirable to invite further increases in the amount of heat for heating the separation claw.